Showing papers in "IEEE Transactions on Biomedical Engineering in 1967"

Miniature Passive Pressure Transensor for Implanting in the Eye

Abstract: A newly developed method for measurement of intraocular and other physiological pressures consists of a novel displacement transducer contained in a distensible pillbox small enough (3 to 60 ?l) to be implanted in the eye of a small laboratory animal. Nothing pierces or even touches the globe. This passive resonant transensor absorbs energy from an oscillating detector coil outside of the animal at a frequency dependent upon the pressure in the eye. Passive operation provides extended life, but limits useful range to less than 10 transducer diameters, which has proved sufficient for intraocular pressure measurement.

Arterial Pressure Pulse Contour Analysis Via a Mathematical Model for the Clinical Quantification of Human Vascular Properties

Abstract: A lumped parameter physical model of the human vascular system is proposed, which consists of four components? two elastic chambers joined by an inertance and followed by a pure resistance (grossly approximating, respectively, large and small arterial systems joined by long columns of blood and followed by the capillary bed). Equations of this model are presented in both mechanical and electrical equivalents and normal modes of response are derived. These normal modes of the model determine a descriptive equation for the contour of the actual arterial pressure pulse. Particular values of model components can be calculated for specific human subjects under varying conditions of stress or disease through a least squares fit of the descriptive equation to the clinically measured pressure pulse contour.

Difference-Differential Equations for Fluid Flow in Distensible Tubes

Abstract: The solution by Womersley of the Navier-Stokes equations for fluid flow in distensible tubes has been most useful to students of hemodynamics. However, this solution requires linearization, and, because results are obtained after transformation into the frequency domain, nonlinear or time-varying effects are not easily added. Analog, hybrid, or digital computer simulation require that difference-differential equations be obtained. This proves to be readily possible by returning to the Navier-Stokes and continuity equations, and using ordinary difference techniques in the space dimensions.

Vectorcardiographic Diagnosis Using the Polynomial Discriminant Method of Pattern Recognition

Abstract: This paper describes research on the application of a newly developed pattern-recognition technique called the polynomial discriminant method (PDM) [1] to the diagnosis of heart disease as evidenced in the vectorcardiogram (an orthogonalized form of electrocardiogram).

Electronic Device for Physiological Kinetic Measurements and Detection of Extraneous Bodies

Abstract: An electronic device is proposed for measuring motion within the human body in the presence of extraneous metallic bodies within it, by reflected environmental changes, near a coil forming part of the tuned circuit-fan oscillator. The circuit details and the various possible applications are discussed.

Neuromuscular Control System

Abstract: Rapid skilled movements by a human subject are executed at such a rate that conscious control can be no more than the strategic selection of a sequence of detailed tactical plans of control, which have previously been learned by the subject. By the use of transient changes in the force applied to various muscle groups, and computer analysis of the responses obtained, it has been possible to observe separately the roles of spinal reflexes, subroutines of motor impulses from the central nervous system, and conscious voluntary control.

The Design and Use of an FM / AM Radiotelemetry System for Multichannel Recording of Biological Data

Abstract: A multichannel telemetry system for EEG recording has been constructed for study of animal or human behavior correlates under natural, unrestrained conditions. To be useful in research of this kind, the transmitted radio signal must be independent of the environment, so that changes in antenna loading and in signal level cause no artifact. Standard IRIG proportional-bandwidth FM subcarrier channels are used. These subcarriers are generated by twin-T oscillators, modulated in turn by the amplified data signals. The FM subcarriers are then linearly summed and impressed upon a crystal-controlled AM transmitter. The system is also relatively insensitive to major shifts in supply voltage. Wherever possible, fabrication was by means of integrated circuits, thus reducing the bulk of the modules.

A Principle for Solving a Class of Anisotropic Current Flow Problems and Applications to Electrocardiography

Abstract: In studies of electrocardiographic lead performance, theoretical analyses of the influence of the anisotropic heart and skeletal muscle are particularly difficult. In this paper, the basic differential equations of static fields and steady current flow are arranged to emphasize the field and conductivity dependent charge distributions which arise in anisotropic media. The equations are applied to two types of problems of immediate interest. Firstly, the equations are used to explain how anisotropic media may be included in current digital computer studies of the heart-lead relation and to conclude that the techniques which made the computer studies possible tend to lose their advantage when applied to arbitrary anisotropic configurations. Secondly, the equations are used to develop a principle which permits exact solutions for the fields of numerous simple anisotropic configurations. Three such configurations useful for heart-lead studies are analyzed with the following results: the anisotropic skeletal muscle can be treated in special cases such as a head-foot heart-vector lead approximately as isotropic with resistivity of 280 ohm cm; the closed dipolar layer in an anisotropic, inhomogeneous heart produces the same null electric field as it does in homogeneous isotropic media; bounds on the influence of the heart's anisotropy on a heart-vector lead field are estimated at plus or minus 12 percent of the average lead field intensity.

Magnetic Susceptibility Meter for In Vivo Estimation of Hepatic Iron Stores

Abstract: An instrument is described for recording linear body scans of magnetic susceptibility in living rats. The sensor is a transformer which employs a toroid core with a large air gap. The magnetic properties of substances within the gap affect the reluctance of the core-gap magnetic circuit, thereby affecting the transformer characteristics. To minimize instability caused by temperature induced changes in core dimensions, the cores were made of the low expansion steel, Invar. The secondary voltage of the measuring transformer is compared with that of a similar reference transformer with differences in this comparison voltage processed by tuned amplification and phase-sensitive detection. The sensitivity of the instrument is limited by zero instability equivalent to ±0.06×10-6 EMU/cm3 over 30 seconds, with a precision of measurement of ±0.03×10-6 EMU/cm3 achieved by output filtering. Studies using live rats demonstrate that with this technique iron-loaded animals can be distinguished from control animals, because the high hepatic concentration of storage iron in the liver of the experimental group exhibits positive magnetic susceptibility. Consideration of the transformer characteristics suggests that similar, safe, and rapid measurements of magnetic susceptibility can be made in humans, although many other factors remain as variables which must be evaluated before such measurements can be used to quantitate iron stores in patients.

Experimental models for current conduction in an anisotropic medium

Abstract: Many biological tissues have some degree of directional organization and would therefore be expected to behave anisotropically to electrical current conduction. An analysis of curren t and poten tial distribu tions throughout the bulk of such a tissue may be required, for exa nrple, in electrical stimulation and recording with macroelectrodes, impedance measurements, and field effects in cerebral cortex. In all these cases the sources and sinks of current will usually have complex distributions which render a cornputa tional solution difficult and inaccessible to experirnental workers, In addition it is normally impossible to construct a model and measure the required quantities since the model would require an anisotropically conducting medium which could not be easily realized in practice. The method described, subsequently, shows it is possible to use a model with an isotropic medium provided the shape of the model is suitably distorted. The method will be outlined for the case of finding the current and potential distributions when a current I is passed between two arbitrarily shaped electrodes in an anisotropic medium having principal conductivities.

On the Sufficiency of Autocorrelation Functions as EEG Descriptors

Abstract: Brain waves or EEG's are the seemingly random voltage fluctuations which appear on the surface of the scalp of humans and animals. The EEG Research Group at the University of Missouri has been interested in finding useful statistics with which to describe an EEG. In the past such calculations as the rms value of the wave, the autocorrelation function, etc., have been used to describe the process. It is convenient to use a stationary random process as a model for the EEG. Because the amplitude distribution of the EEG appears to be Gaussian, it has been suggested that a better model might be the normal stationary random process. This paper describes a test which was made to determine if the normal process is really a good model for the EEG.

The Effect of Prior EEG ``Coupling'' Upon the Visual Evoked Response

Abstract: A unique statistical technique is described which appears to measure important interaction processes within the central nervous system (CNS). This statistic, termed ``weighted-average coherence,'' or C?, is derived primarily from parameters generated in cross-spectral frequency analysis. C? has the useful property, however, of summarizing a larger amount of cross-spectral information into a more manageable form. By applying C? analysis to the ongoing electroencephalogram (EEG), it has been possible to define unique patterns of interaction, or ``coupling,'' between different brain areas. The total pattern of EEG coupling is taken to define a given state of functional brain organization. Moreover, since C? is sensitive to changes in the EEG, it also reflects something of the dynamic properties of such brain organization.

The Detection of Cortical Spike Activity at the Human Scalp

Abstract: Spike activity has a much wider energy spectrum than does postsynaptic activity. Under the assumption that the frequency spectrum of spike activity ranges from dc to 1000 Hz, the prediction was made that high-frequency electrical activity could be modulated by sensory stimulation and might well be detectable at the human scalp. This prediction was borne out in experiments that were successful in detecting the modulation of activity between 300 and 1000 Hz. This band was selected to suppress the major effects of the low-frequency classical brain waves. A control experiment was conducted in which any surviving harmonics of the classical evoked potential were markedly reduced. The high-frequency activity was essentially unaffected, thereby substantiating the hypothesis that this kind of activity is different from brain waves. It was also shown that the effect is related to the specific frequency of the stimulus and it is not attributable to either a general increase or a redistribution of brain activity. It is suggested that the high-frequency or spike activity might furnish the basis for a better correlation between electrophysiological data and sensory experience than does the classical evoked response.

Histologic Changes in Continuous, Long-Term Electrical Stimulation of a Peripheral Nerve

Abstract: The chronic stimulation of peripheral nerves has, in the past, usually been of an intermittent or relatively short-term nature. Histologic changes which have taken place have been attributed to the trauma caused by mechanical factors and/or the effects of electrical charges. Investigators, speculating on the effects of electro-stimulation, have designed electrodes specifically to minimize tissue damage. The purpose of the present investigation is to determine which pathologic alterations, if any, are caused specifically by electrical?as distinct from mechanical?factors. Dogs were divided into two groups, differing only in that one group?the controls?had electrodes implanted around the phrenic nerve, but stimulation was never applied. Duration of the test was up to 308 days. The results indicated that no histologic alterations could be attributed specifically to electrical stimulation, as contrasted to mechanical trauma, to the phrenic nerve.

Crosscorrelation Techniques Applied to the Electrocardiogram Interpretation Problem

Abstract: A study was made to see if a single, easily-recorded electrocardiogram lead can be used?employing a crosscorrelation scheme?to screen abnormal adult ECG waveforms from normal waveforms. The study also sought to classify the abnormal waveforms into their respective disease categories. Standard lead I (the potential from left to right arm) was chosen for the study. Only the QT interval, the part of the heart cycle resulting from the electrical activity of the ventricles, was studied. In addition to ``normal'' ECG waveforms, four cardiac diseases were studied: right and left bundle branch block; and right and left ventricular hypertrophy.

Transients in Carbon Dioxide Stores

Abstract: Physiologically correct models of the respiratory control system require accurate knowledge of the structure and dynamics of carbon dioxide stores of the body. Several models of these stores have been investigated and the computed results compared to experiment. The effect on these models of alterations in cardiac output, regional perfusion, and tissue absorptive capacity for carbon dioxide has been examined. Experimental results are best duplicated by a five venous compartment model of carbon dioxide stores with a low absorptive capacity for carbon dioxide during the first few minutes following a change in ventilation.

Evoked Potential Recording: An Adjunct to Human Stereotactic Surgery

Abstract: The localization of various brain structures during stereotactic surgery is dependent upon stereotactic atlases used in conjunction with demonstrable radiographic landmarks. Because of the considerable anatomical variability encountered in humans, this localization is only an approximation. For animal studies electrode positions can be confirmed histologically at necropsy. Routine techniques have been developed for animal neurophysiologic recording but have not been extensively applied to humans. This paper presents a method for recording human evoked potentials from various thalamic nuclei. Peripheral stimulation and stimulation within the brain are used to evoke depth and scalp potentials. The evoked responses are averaged at various well-known thalamic nuclei, e.g., ventral posterior lateral (VPL), ventral posterior medial (VPM), centre median (CM), that have characteristic responses. These nuclei, in conjunction with radiographic information, are used as landmarks to aid location of other brain structures.

A Six Channel Physiological Telemetry System

Abstract: A six channel FM/FM physiological telemetry system was designed to measure two surface temperatures, an internal temperature, the respiration rate, and position and muscle spasm of a paralyzed patient. The system has since been adapted to permit the measurement of pulse rate. Tunnel-diode subcarrier oscillators operating from a constant-current source provided excellent temperature and long-term stability while permitting a complete transmission package with size 0.6×2.5×2.5 inches and weight 15 gm. A compatible transistorized receiving system was also constructed.

The Sampling and Analysis of Lead Fields in Electrocardiographic Torso Models

Abstract: Reciprocal energization of an electrocardiographic lead connection in a torso model produces an electrical field from which equivalent cardiac dipolar and multipolar transfer coefficients may be determined. This purpose can be fully served by sufficiently numerous experimental measurements of reciprocal field potential over a Gaussian sphere which is large enough to encompass the entire cardiac region. A systematic field-sampling procedure of appropriate design has resulted in the development of reliable numerical methods for the resolution of reciprocal potential functions into the desired transfer coefficients. The underlying principles as well as the data reduction procedure itself are directly applicable to the analysis of other kinds of Newtonian potential functions.

Dielectric Properties of Osmium-Fixed Erythrocytes

Abstract: The deterioration of the membranes of osmium-fixed erythrocytes after washing in distilled water is demonstrated by a marked drop in membrane resistance and an increase in permeability of the cells to small solute molecules. Yet when these cells are placed in dilute salt solutions their conductivity remains high. The lower limit of the cell conductivity is presumably determined by the counterions of the fixed charges within the cell. Both the stability of the membrane and the fixed charge concentration within the cell are found to depend upon the pH of the fixing solution used for preparation of the cells.

An electromagnetic biopsy device

Abstract: This communication describes an electromagnetic biopsy device built at the Electronics Department of the Weizmann Institute, Israel, and presently undergoing evaluation at Tel-Hashomer Hospital. The device is intended to obtain biopsy samples froom the gastrointestinal tract after introduction through the natural openings to this tract. It wras originally intended to develop a device which would be easily passed, would be capable of taking multiple cuts without having to be withdrawn and reset after each cut, would not accidentally trip while being directed to the site of interest, could be backed off an incomplete cut and would permit the degree of vacuum to be con-trolled independently of the force activating the knife. This latter condition allows better control of the size of the biopsy speclimen than is achieved with several available devices.

Self-Synchronizing Cardiac Pacemaker

Abstract: A new kind of cardiac pacemaker for direct heart stimulation in cases of intermittent or variable heart block is presented. The pacemaker is capable of providing stimuli either synchronously with ventricular depolarization or at a fixed rate when natural pacing fails. Thus any competition between artificial and physiological rhythm is avoided, while allowing the exploitation, from the hemodynamic viewpoint, of the surviving capability of physiologic control of the heart rate. The main features of the instrument are that the shifts from synchronous to free operation and vice versa take place in an automatic way, and no electrode besides those which provide stimulation are needed for synchronization. The mean power consumption of the pacemaker is comparable with that of conventional unsynchronized pacemakers. Thus the subcutaneous implantation is possible, with a theoretical lifetime of 30 000-hour autonomy. Schematic diagrams and waveforms are included.

On a Mathematical Theory of Decompression

Abstract: A theory is presented on the decompression procedure required after diving and on the accumulation of gases in the blood and in tissues during a dive. It is postulated that the decompression procedure must be such that at no time the partial pressure of the dissolved gases exceeds the external pressure. It is shown that the partial pressure of dissolved nitrogen is a weighted average of the external pressures to which the diver has been exposed previously. To make allowance for the partial pressure of dissolved oxygen, however, requires a more complicated formulation. The theory is in good agreement with published diving tables.

Green's theorem and potentials in a volume conductor

Abstract: In their recent paper Barr, Pilkington, Boineau and Spach (ibid., vol. BME-13, pp. 88-92, April 1966) present a method for solving the boundary-value problems of interest to electrocardiography based on Green's theorem. An earlier method was presented Gelernter and Swihart (1964) and the purpose of this note is to point out how it also can be related to Green's theorem. A more extensive treatment of aspects of this problem is contained in a recent preliminary report by the author (MIT, Research Lab. of Electrollics, Cambridge, MA, Quarterly Progress Rept. 81, pp. 218-226, April 15, 1966. also Biophys. J., January 1967).

FM/FM Multiplex Radio-Telemetry System for Handling Biological Data

Abstract: Multiplex systems are examined in the time and frequency domains for their utility in applications to biological studies. The continuous-wave FM is shown to fit best the requirements of genuine signal reproduction, reasonable construction and reliability.

Mathematical Analysis and Application of Iron-Wire Neuron Model

Abstract: A mathematical model for the behavior of passive iron in concentrated nitric acid, based on the electrochemical mechanism, is proposed. The model is capable of explaining several phenomena including threshold for activation, monostable property, periodic activation, propagation of activation and threshold for propagation. Furthermore, the mathematical model shows that the electrochemical active line has a specific propagated waveform and velocity of propagation.

Parametric Sensitivity of Physiological Systems- Prognostic Analysis

Abstract: Prognostic analysis is a procedure for studying a broad class of multivariable dynamic physiological systems with respect to parametric changes. The technique is basically an application of sensitivity analysis and leads to a computer method for extrapolating the observed behavior of a system for a range of parametric deviations about their nominal values due to operational malfunctions.

Computer Equalization of Low-Frequency Components in Tape Recorded Electrocardiographic Signals

Abstract: Low-frequency equalization of a digitized electrocardiographic waveform has been accomplished by adding to the waveform several of its integrals, appropriately weighted. The weighting factors required for correction of distortion produced by a particular amplifier are initially obtained from a least squares correction of its step response. Neither analysis of the amplifier circuit, nor frequency-response testing is necessary.